Coating of gelatin silver halide photographic emulsions



United States Patent Oflice 3,516,844 Patented June 23, 1970 U.SL Cl. 117-34 7 Claims ABSTRACT OF THE DISCLOSURE In manufacture of photographic papers and the like wherein a photographic silver halide emulsion is coated on a baryta surface, coating speeds can be substantially increased by including in the baryta layer a surface active agent which is a condensation product of an alkylene oxide with a straight chain or branched chain alcohol or an alkyl phenol.

This invention relates to preparation of coated photosensitive recording materials and particularly to highspeed coating of photographic films and papers.

A widely-used type of sensitive photographic element comprises a support, usually paper, bearing a baryta layer over which is coated a photographic silver halide emulsion layer. Usually the baryta layer and the emulsion layer comprise hydrophilic colloid which may be gelatin or other suitable materials.

In the past few years, improvements have been made in coating techniques and machinery, for example in hopper coating, that permit increased speeds for coating of photographic emulsions on photographic supports. Higher speeds for coating have raised new problems not previously encountered; for example, in coating of conventional gelatin-silver halide photosensitive emulsions on a baryta coated support, surface imperfections on the coated layer were found to occur more frequently as coating speeds were increased. Such surface imperfections on the emulsion coating will lead to consequent imperfections in finished photographs made with the photographic element.

Saponin has been widely used in the past as a coating aid incorporated in baryta layers and photographic silver halide emulsion layers to improve coating characteristics. As coating speeds for suction slide hopper coating machines have been increased past about 100 lineal feet per minute, local imperfections of the kind described have been found to occur too frequently using conventional emulsions with saponin. An object of the present invention is to provide improvements using coating aids that will improve the finished surface characteristics of a gelatin-silver halide emulsion coated on a baryta layer at coating speeds in excess of 100 lineal feet per minute. According to the present invention, local imperfections in gelatin silver halide emulsions coated on baryta layers, by high-speed coating processes employing coating speeds in excess of 100 lineal feet per minute, and particularly mottled surface of the coating due to high coating speeds, are substantially reduced or eliminated by means of certain coating aids which are incorporated in the baryta layer; such coating aids consist essentially of a condensation product of an alkylene oxide containing 2-4 carbon atoms with a straight or branched chain alcohol or an alkyl phenol, said product containing from 4-15 condensed alkylene oxide units. In preferred embodiments of the invention, the coating aid is present in concentrations from about 0.001 to about 0.5 percent by volume based on the volume of the baryta coating slurry. Coating aids of the class described above are nonionic surface active agents and are available from various manufacturers. An especially preferred coating aid for highspeed application of gelatin silver halide emulsion layers on baryta in accordance with the invention is the series of coating aids sold under the trade name Texofor FN which are nonyl phenol-ethylene oxide condensation products.

In processes according to the invention, a coating aid of the kind described above is incorporated in an aqueous baryta coating preparation which is coated on a suitable support such as paper by any suitable baryta coating procedure. The coating aid apparently prepares the baryta surface for rapid and uniform acceptance of a gelatin silver halide aqueous emulsion to be coated thereon at high speeds. The exact mechanism of the improvement is not clear but from operation of coating procedures with and without the coating aid, we have noticed that baryta layers incorporating the coating aid can be shown to have better wettability and these layers appear to stabilize the meniscus at the bead where the emulsion coating is applied. Without the coating aid, the bead is observed to pulsate at the meniscus at high speed, apparently due to uneven absorption by the baryta surface as the emulsion is applied thereto. With the coating aid, the meniscus does not pulsate, indicating more consistent acceptance of the coating by the baryta layer.

The invention willbe illustrated by detailed description of some preferred modes of carrying out the invention in the following examples.

EXAMPLE I An aqueous baryta slurry containing 1 part of gelatin for 9 parts of baryta is prepared. A condensation product of ethylene oxide with nonyl phenol containing eight ethylene oxide units (Texofor FN 8) is added in concentrations between 0.01 and 0.4 percent vol./vol., the baryta composition coated onto a paper support, dried and the dried-down baryta layer is overcoated by a highspeed hopper coating machine with a photographic silver bromide emulsion layer. A final concentration of 0.1 percent of Texofor FN 8 in the baryta layer increased the critical speed at which the emulsion could be coated without significant surface defects from 200 ft./min. to the maximum speed of the machine 250 ft./min. On another coating machine the speed was increased from 200 ft./min. to 330 ft./min.

EXAMPLE II The procedure of Example I was repeated employing the condensation product of ethylene oxide with nonyl phenol containing 11 ethylene oxide units (Texofor FN 11) at concentrations between 0.005 and 0.2 percent by volume to increase the speed at which the emulsion could be coated thereover without defect-A concentration of 0.1 percent increased the useable coating rate for the emulsion from 200 feet per minute to 245 feet/min. on one machine and from 200 feet/ min. to 330 feet/ min. on another machine.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from th spirit and scope of this invention.

I claim:

1. In a method of making a photographic element comprising the steps of coating a support with an aqueous baryta slurry, drying the coated support, and coating a gelatin-silver halide emulsion on the baryta layer, the improvement wherein maximum tolerable coating speeds are substantially increased by incorporating in said baryta slurry from about 0.001 percent by volume based on the volume of the baryta slurry of a nonionic surface active agent selected from condensation products of an alkylene oxide containing from 2-4 carbon atoms with a member selected from the group consisting of straight and branched chain alcohols and alkyl phenols, said condensation product containing from 4 to 15 condensed alkylene oxide units.

2. The improvement defined by claim 1 wherein said surface active agent is the condensation product of ethylene oxide with an alkyl phenol.

3. The improvement defined by claim 1 wherein said surface active agent is the condensation product of ethylene oxide with nonyl phenol.

4. The improvement defined by claim 3 wherein said surface active agent is the condensation product of ethylene oxide with nonyl phenol containing 8 ethylene oxide units.

5. The improvement defined by claim 3 wherein said 7. The improved method defined by claim 1 wherein said tolerable coating speeds are increased substantially to maximum tolerable coating speeds above lineal feet per minute.

References Cited UNITED STATES PATENTS 3,044,874 7/1962 Popeck et al 96114 X 2,823,123 2/1958 Knox 96-94 2,835,609 5/1958 Starck 11734 X 3,018,178 1/1962 Harriman 1l734 X 3,158,484 -11/l964 Willems et a1 96-114 X 3,210,191 10/1965 Willems et al 117-34 X 3,255,013 6/1966 Dersch et a1 96-114 X FOREIGN PATENTS 684,040 Great Britain.

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R.

1l77l; 96--l 14, 114.5 

